This invention relates to methods and compositions useful in the treatment and recycling of waste coating color that is generated in paper coating processes. Coatings are commonly used during the papermaking process to improve the optical and printing properties of the resulting paper. Coating colors or formulations commonly include pigments, binders, and other minor additives. Pigments can represent as much as 95% of the solids in the coating formulation and contain calcium carbonate, kaolin clay, titania, talc, plastic pigments, silica, alumina, or mixtures thereof. Binders typically represent from 5% to 25% of the solids in the coating formulation and are natural or synthetic polymers that bridge the pigment particles in the coating to give the coating cohesive strength and flexibility. The most typical natural binder is starch, while typical synthetic binders are styrene-butadiene copolymers, styrene-acrylate copolymers, polyvinyl alcohol, and polyvinyl acetate. Minor additives usually make up about 1% of the solids in the coating formulation and consist of a variety of chemicals that serve many purposes in the coating. Possible additives are insolubilizers, optical brighteners, dispersants, lubricants, defoamers, rheology modifiers, dyes, and microbiocides. The coating forms a layer on the outside of the sheet of paper. This improves its opacity, brightness, smoothness, and print quality compared to an uncoated sheet.
Unfortunately, significant amounts of waste coating color are generated in typical paper coating processes. This waste is a result of coating that has been added to the process but which for one reason or another does not end up coating the paper surface. In some cases this waste can be as much as 4% of the total applied coating. Common practice is to dewater and compact this waste coating and to simply dump it into landfills or burn it. Many mills use hundreds of thousands, if not millions of tons of coating, resulting in tens of thousands of tons of waste being generated annually. This results in both terrible environmental costs as well as a significant waste of economic resources. Thus there is clear need and novel utility in a method of recycling coating waste generated in a papermaking process. The art described in this section is not intended to constitute an admission that any patent, publication or other information referred to herein is “Prior Art” with respect to this invention, unless specifically designated as such. In addition, this section should not be construed to mean that a search has been made or that no other pertinent information as defined in 37 CFR §1.56(a) exists.